This project is concerned with the normal cycle of renewal and degradation of the outer membranes of mammalian photoreceptor cells. Renewal of the outer segments is studied by tracing the synthesis and localization of the principal protein opsin; our approach to this is to add radioactive precursors to bovine retinas in vitro, and trace the appearance and disappearance of opsin or "pro-opsin" in enzymatically defined subcellular fractions; the major obstacle presently is obtaining one or more specifically identifiable peptides of opsin, and we are attempting to do this by a variety of techniques, including column and paper chromatography of peptides which have been obtained by cyanogen bromide or enzymatic cleavage and then reacted with NH2 reactants, including FDNB and dansyl chloride. Degradation of outer segment membranes is studied by enzymatic characterization of subcellular fractions of bovine pigment epithelium--particularly lysosomes--obtained by centrifugation of cell homogenates on linear sucrose density gradients. The subcellular fractions are assayed for a variety of lysosomal marker enzymes, and for their activity in degrading outer segment membranes which had been previously prepared with radioactive amino acids, sugars and fatty acids.